Numerous, high volume manufacturing applications exist in which UV light sources are used as part of the manufacturing process for spot curing of UV activated adhesives or other materials. Typical examples of processes that use UV spot light sources for adhesive curing, include lens camera module assemblies used in cellular telephones, and hard disk drive pick-up assemblies. The parameters of these manufacturing processes are tightly controlled to ensure high product quality and predictable manufacturing yields. It is not uncommon, for instance, for a single manufacturing plant to have hundreds of separate UV light sources. Typically it is difficult to ensure the consistency of the output of these myriad of light sources, both in unit-to-unit comparisons, as in comparisons within a single unit taken over an extended period of time. In addition, cost becomes a significant factor in equipping a manufacturing facility with sophisticated, stand-alone curing systems.
Tight control of the manufacturing processes places specific requirements on the equipment used on the manufacturing line. For UV light sources, this typically includes an ability to adjust the optical output of the light source. Adjustment is required during the process development stage of the manufacturing process to optimize the curing parameters. While process optimization is being performed, typically only a small number of curing systems are used. Once the process has been performed, the parameters such as the flux of light and exposure time are recorded. In order for this process to be replicated on other curing systems, the UV curing system must have first the means to generate the light, a means to regulate when and how much light is delivered to curing site, a means to program and store these parameters within the unit, and a processing means to read the stored parameters and execute the curing process when required. In addition, more advanced systems offer the ability to regulate the optical output over the course of multiple exposures to ensure that degradation in the UV light source, over time, e.g. due to aging effects, does not influence the curing process.
In such systems, where each light sources is associated with its own controller, e.g. at each individual workstation, each light unit must be individually calibrated, and adjusted to set or store process parameters, thus requiring monitoring and calibration to ensure consistency and provide a highly repeatable operation across a single or multiple work stations.
Closed loop feedback UV curing systems are available in either relative or calibrated form. In the relative form, the closed loop feedback signal is a relative measure of the output of the UV system or some other surrogate indicator of output. For the more advanced systems, the feedback signal is measured in absolute units, such as Watts (see for example, U.S. Pat. No. 5,521,392 to Kennedy. The advantage of calibrating a closed loop feedback signal is that it allows for the easy programming and monitoring of the curing process on multiple UV curing units, which as discussed above, is a difficulty within manufacturing facilities utilizing many UV systems, &/or multiple systems located at geographically distant facilities.
For example, a “Method for calibrating light delivery systems, light delivery systems, and a radiometer for use therewith” is described in U.S. Pat. No. 7,335,901 to Kayser (AP1224US) and US Patent publication no. 2008/0197300 to Kayser (AP1224US CIP), which are commonly owned with the present invention. The handheld portable radiometer disclosed therein facilitates monitoring and calibration of light sources, which may be e.g. conventional mercury lamps or LED arrays. Each light source has its own control system for operation and programming, requiring that each light source has a significant amount of intelligence and processing power.
The features described above result in complex and expensive curing systems, each of which must be separately calibrated, monitored and programmed.
Efforts by industry to date to reduce the cost of these systems can be divided into two categories. The first category involves creating multiple sources of UV light controlled by a single control unit. For example, this may be achieved either by taking a single, higher powered light source such as a mercury arc lamp (typical optical power generation of >10 W), and dividing the energy provided by the lamp between multiple light delivery means, such as bi- or multi-furcated optical light-guides. Alternatively, several lower powered sources of UV light, such as UV LEDs (typical optical power generation of <2 W), may be connected to the same controller. The controller in this latter case can provide control signals and function to monitor the individual sources, or it can also provide electrical drive power to the individual sources. Another approach to reduce the cost of UV curing systems has been to sacrifice features, typically by reducing the control capabilities of each unit. However, this approach results in less control of the manufacturing process.
In known systems for controlling a plurality of light sources, each light source has limited functionality, and a central control system contains intelligence for control of multiple light sources. For example, Hamamatsu has introduced a networked LED system with a controller based on LED's. This system has the advantage of being able to control multiple UV light sources (i.e. up to 8 units) independently and simultaneously, but suffers from the limitation that the light sources must be spatially located within the length of the intervening connecting cable. In addition, the fixed and central location of the controller in the LED light source network makes it difficult to perform optical calibrations of the individual UV LED light sources. Calibration must be performed with a separate radiometer unit, the radiometer signal either manually or electronically being fed back to the controller unit. As mentioned above, such a system only partially addresses the above-mentioned problems of monitoring, calibrating, and controlling or programming tens or hundreds of light sources in a manufacturing environment.
Thus improved systems and methods are needed for managing a large number of light sources for photo-curing applications, particularly in a manufacturing environment requiring tight control of process parameters for consistency in processing, and/or where the light sources may be distributed at workstations over a large area, or located in multiple geographic locations, so as to allow for a highly repeatable operation across a single or multiple work stations